1. Field of the Invention
The present invention relates to an electrophotographic apparatus, and more particularly to a high-voltage power source for supplying a high voltage to corona dischargers employed in the electrostatic latent image forming step, and the image transfer step etc., in a copier or in an electrostatic recording apparatus.
2. Description of the Prior Art
In an electrophotographic apparatus for obtaining a reproduced image by optical scanning of an original such as a copier, there are employed corona dischargers for various purposes such as a primary charger employed in the formation of the electrostatic latent image on a photosensitive member, a transfer charger for transferring the obtained image onto a transfer sheet, a liquid squeezing discharger in the liquid development process, and a charge eliminator for dissipating the potential on the photosensitive member.
FIG. 1 shows, in a schematic perspective view, the arrangement of a conventionally known photosensitive drum, corona dischargers and a high-voltage power source in such an electrophotographic copier, wherein said components are supported by unrepresented side plates of the copier.
In FIG. 1, around a photosensitive drum 1 there are provided dischargers 2a, 2b and 2c which are respectively connected to connectors 3a, 3b and 3c and further connected through high-voltage cables 4a, 4b and 4c to a high-voltage power source 5, which in turn receives a power supply through input lines 6 and is grounded to the body of the copier through a grounding terminal 7. The photosensitive drum and the casings of the dischargers are similarly grounded to the body of the copier.
Such conventional arrangement is known to have various drawbacks as explained in the following.
Firstly, such conventional arrangement is apt to generate noise. It is to be noted that electronic control utilizing integrated circuits or large-scale integrated circuits are widely used in recent years in copiers and similar apparatus, and for this reason it has become extremely important for avoiding erroneous functions of the control mechanisms to minimize the noise generation inside the apparatus.
However, the conventional high-voltage cables as shown in FIG. 1 tend to become the source of noise, functioning as an aerial. Although the use of shielded cables will prevent such noise generation, such shielded cables are not only expensive themselves but also require additional costs for the cable holders they require and for the high-voltage connector required for each of the corona dischargers. Also the use of such cables results in a considerable useless leak current resulting from the electrostatic capacitance between the cables and ground.
In addition, in an apparatus as shown in FIG. 1, there is required a structure allowing the extraction of the photosensitive drum from the apparatus for the purpose cleaning or replacement of said drum. For this reason the high-voltage cables leading to the corona dischargers are located generally at the rear side of the apparatus which is opposite to the direction of drum extraction, and the drive system for the copier is also located at said rear side. It therefore becomes necessary to provide sufficient space for the high-voltage cables for ensuring mechanical and electrical safety between the drive system and the high-voltage cables. Also there should be provided sufficient space for the discrete high-voltage connectors for various corona dischargers positioned around the photosensitive drum. Consequently the presence of such cables and connectors has been a serious obstacle to the compactization of the apparatus.
Also in a corona discharger, as the discharge current between the discharging wire and the casing of the discharger is larger than that between said wire and the photosensitive drum, it is desirable for the purpose of noise prevention that said casing is positioned close to the grounding terminal of the high-voltage power source. However the grounding is generally achieved through the body of the copier, and such arrangement increases the impedance of the high-voltage circuit and is not desirable for noise prevention.